


Joined Jan 2012
146 Posts

Quote:
Based on his numbers when I plug it in, I get a CG position of 28.50 (28.4963) inches from the tip of the spinner or 8 (7.9963) inches from the Mains What formula are you using? 



Joined May 2017
11 Posts

This is an interesting discussion. And Curiosity Killed the Cat. So I experimented FWIW.
With my unfinished fuselage, just 2 servos in the tail I did some weighing. First fuselage with main gear on floor for all readings, scale on floor with tail wheel on scale. Fuselage not level. 250g 8 7/8 0z. Next, fuselage level. Scale on adjustable table, tail wheel on scale. 282g 10 oz. Next, fuselage level. Scale on floor, wooden prop to level fuselage, scale reading zeroed for tare weight, tail wheel on wooden prop. 283g 10 oz. Interesting. 



OK, I measured once again after adding 5 pounds to the forward fuse.
Weight # Dist inch Main Gear 1 13.8 21.5 Main Gear 2 14.5 21.5 Tail Gear 3.0 84 CG 31.3 27.49 Current Balance Point from Tip of Spinner 27.50 Proper Balance Point from Tip of Spinner I talked to Wendell Hostetler and he did not recall adding any weight using the same setup to get it to balance. I simply cant believe I need to add 5 pounds of weight to achieve proper balance with an all up weight of 31 pounds. 



here's my question...how does it balance at 30% MAC? You have a constant chord wing which makes locating 30% of chord very easy, ( wing chord x .3 = distance from leading edge ) and that's a good starting point and should be fine for a maiden.



Joined Jan 2012
146 Posts

Quote:
Where is the recommended CG measurement point? I guess an alternative is to use this other unit that I also have used the EZ Balancer 2 




Quote:
I have a Xicoy CG balancer and also a spreadsheet that I created where the spreadsheet numbers exactly match the Xicoy numbers. Using the numbers you first posted, the span from the front mains to the tailwheel is 62.5". The critical number I do not have is the distance from the front mains to the manufactures recommended CG point. If you would supply me with that number I will plug the info into my calculator. If you do not have that number, let me know the distance from the front mains back to the wing tube. As calculated now the (actual CG) of the airplane is 7.00 inches behind the front mains. Remember the actual CG measurement may or may not be the correct balance point based on other critical input. However, if your manufactures CG does fall 7 inches behind the front mains, then your plane is exactly balanced. I suspect the correct CG balance point will fall about 6 inches behind front mains. If it does then your plane will be considered tail heavy. Jaketab 




Finally had time to get back to work on the RV4.
I added about 2.8 pounds to the nose and the numbers came out as follows. Distance to Main Gear: 21.5" Distance to Tail Wheel: 84.0" Right Main Weight: 12.72 lbs. Left Main Weight: 13.33 lbs. Tail Wheel Weight: 2.79 lbs. Total Weight: 28.84 lbs. Calculations indicate CG is 27.55" behind spinner bolt. Recommended CG is 27.50" behind spinner bolt. So, just a bit tail heavy. 



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Thanks Jaketab. I appreciate the confirmation. Makes me feel a little more confident.




Post #6 in this thread on RCGroups is what I use and it works great.
The plane has to be level as if it was flying straight and level. https://www.rcgroups.com/forums/show...caleAirplanes 




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